1. Field of the Invention
The present invention generally relates to a system and method for providing a presence subscription delegation service in a Session Initiation Protocol (SIP)-based presence system. More particularly, the present invention relates to a presence subscription delegation service that can be provided in a multi-domain environment as well as in a single-domain environment.
2. Description of the Related Art
Presence service is a service of collecting information about the current status of a user's communications from a set of devices and providing the information to another user. The user that is watched is called presentity, the communication status information is called presence information, and the user that receives the presence information is called a watcher.
An SIP-based presence service is implemented using RFC 3856 “Presence Event Package for the SIP” based on RFC 3265 “SIP-Specific Event Notification”.
FIGS. 1A and 1B are a diagram illustrating a signal flow for a conventional SIP-based presence service.
Referring to FIGS. 1A and 1B, a watcher 100 transmits a request for SIP SUBSCRIBE to Presence Event to a presentity's presence server 120 via a Session Initiation Protocol/Internet Protocol (SIP/IP) core 110 in order to receive presence information about a presentity in steps 1 and 2. The presence subscription request for the presentity is realized by an SIP SUBSCRIBE message for presence event with “Request Line” set to <presentity URI>, “To header” set to <presentity URI>, “From header” set to <watcher URI>, and “Contact header” set to “watcher's contact URI”.
Upon receipt of the presence subscription request from the watcher 100, the presence server 120 performs presence authorization according to a presence authorization rule of the presentity in step 3. The presence authorization includes presence subscription authorization for determining whether the presentity permits presence subscription to the watcher and presence content authorization for determining presence information to be delivered to the watcher, if the presentity gives permission to the watcher.
After successful presence authorization, the presence server 120 transmits an SIP 200 OK message to the watcher 100 via the SIP/IP core 110 in steps 4 and 5 and establishes an SIP session for presence event between the presence server 120 and the watcher 100 in step 6.
When the SIP session setup is successful, the presence server 120 transmits presence information about the presentity to the watcher 100 via the SIP/IP core 110 by an SIP NOTIFY message for presence event in steps 7, 8 and 9. The SIP NOTIFY message has “Request Line” set to <watcher's contact URI>, “To header” set to <watcher URI>, “From header” set to <presentity URI>, and “Contact header” set to <presence server's contact URI>. That is, the SIP NOTIFY message is delivered by the SIP session for presence event established between the presence server 120 and the watcher 100.
The SIP NOTIFY message includes, in its body, presence information about the presentity that the presence server 120 intends to transmit to the watcher 100.
Upon receipt of the SIP NOTIFY message, the watcher 100 transmits an SIP 200 OK message to the presence server 120 via the SIP/IP core 110 to indicate the successful reception in steps 10 and 11.
Each time the presence information about the presentity is updated, the presence server 120 transmits the updated presence information to the watcher 100 by an SIP NOTIFY message configured in the same manner as the initial SIP NOTIFY message in steps 13 and 14 and the watcher 100 receives the SIP NOTIFY message in steps 15 and 16.
A new requirement for the conventional presence service has emerged. That is, the watcher 100 should be capable of presence subscription on behalf of another user. This is called presence subscription delegation. The user delegates the right to request presence subscription for him to the watcher 100 and thus the watcher 100 receives presence information about a presentity authorized to the user rather than presence information about a presentity authorized to the watcher 100. However, the conventional presence service cannot provide the presence subscription delegation service.